Can I set a specific default time for a Django datetime field?

From the Django documents for Field.default:

The default value for the field. This can be a value or a callable
object. If callable it will be called every time a new object is
created.

So do this:

from datetime import datetime, timedelta

def default_start_time():
    now = datetime.now()
    start = now.replace(hour=22, minute=0, second=0, microsecond=0)
    return start if start > now else start + timedelta(days=1)  

class Something(models.Model):
    timestamp = models.DateTimeField(default=default_start_time)